How to create big reflective dark glass
If you are a beginner, an easy shader to get good results will be the Principled BSDF, it's a little different than other shaders, you can google it to know more, here is a example:



Keep in mind that if you want glossy objects to look good or realistic, you will need reflections from somewhere, in my example I used a HDRI map to my world shader, I post here to help any guys out there, but it's not a beginner node tree mind you. Essentially what you want is, a image texture to light your scene and also reflect on it.



For you to better understand HDRI maps, maybe these links will help you:

https://www.hyperfocaldesign.com/tutorials/blender-hdri-tutorial-cycles/

https://www.creativeshrimp.com/hdr-lighting-in-blender.html

https://blenderartists.org/t/beginner-professional-lighting-in-blender-2-78-using-hdri/677353

http://hdrmaps.com/blog/blender-hdri-setup/

Hope it helps,

Edit: Here's the file with a better bench topology,



Notice that for you to access the world shader, you need to click on the little globe icon in the node editor. That's where the magic happens with HDRIs.


Also I packed the HDRI maps in the blend file. But If you or anyone reading this, want some free quality HDRIS, here a great source:

https://hdrihaven.com/hdris/

Cheers,